THE TRAPPING OF FLY-ASH PARTICLES IN THE SURFACE LAYERS OF SPHAGNUM-DOMINATED PEAT

The movement of fly-ash particles in a sequence ofSphagnum moss was studied in laboratory experiments and field investigations. The data obtained in the laboratory show that only 0.8% of particles, placed on the surface of a 6–10 cm thickSphagnum layer, were washed out with water (700–750 mm) during the 241 days of the experiment. The majority of added particles were fixed in the upper part (90% in 1–3 cm) of the moss layer. A SEM study indicates that sorption is slightly species-dependent due to the micromorphological parameters of theSphagnum species. The storage of particles bySphagnum mosses allows the use of natural sequences to study the history of atmospheric pollution. The distribution of particles in the upper part of moss layers in Viru Bog (50 km east of Tallinn, North Estonia) shows good agreement with the known air pollution history in Tallinn.     

Changes in microbial community structure and function following Sphagnum peatland restoration

This study examines the recovery of the microbial compartment following active restoration of a North American ombrotrophic peatland extracted for horticultural peat-based substrates and restored by the Sphagnum moss transfer method. We used phospholipid fatty acids (PLFAs) to portrait the microbial community structure and Community Level Physiological Profiles (CLPP) to describe the functional diversity of the microbial communities. Our results indicate that the PLFA profiles were different between the beginning and the end of the growing season, but that it was impossible to distinguish five different vegetation classes found along the disturbance-recovery gradient on the basis of the microbial community structure. The pH, the cover of mosses, Ledum groenlandicum and Eriophorum vaginatum var. spissum were the best environmental predictors for the PLFA composition. The newly formed peat found in aerobic conditions beneath restored Sphagnum carpets had the highest decomposition capacity, whereas the lowest rates were found in the surface samples of non-restored conditions or in the deepest horizons of the natural samples. A large proportion of the variation in the physiological profiles was explained with variables related to the vegetation cover, the physicochemical environment and the microbial structure of the community, which is very promising for future monitoring studies. Overall, this study demonstrates that the recovery of particular plant groups, namely mosses and shrubs in restored peatlands might be the driver of changes occurring in the structure of the microbial communities in restored peatlands.     

Are cadmium, lead and mercury concentrations in mosses across Europe primarily determined by atmospheric deposition of these metals?

Purpose

This study aimed at investigating correlations between heavy metal concentrations in mosses and modelled deposition values as well as other site-specific and regional characteristics to determine which factors primarily affect cadmium, lead and mercury concentrations in mosses. The resulting relationships could potentially be used to enhance the spatial resolution of heavy metal deposition maps across Europe.

Materials and methods

Modelled heavy metal deposition data and data on the concentration of heavy metals in naturally growing mosses were integrated into a geographic information system and analysed by means of bivariate rank correlation analysis and multivariate decision trees. Modelled deposition data were validated annually with deposition measurements at up to 63 EMEP measurement stations within the European Monitoring and Evaluation Programme (EMEP), and mosses were collected at up to 7,000 sites at 5-year intervals between 1990 and 2005.

Results and discussion

Moderate to high correlations were found between cadmium and lead concentrations in mosses and modelled atmospheric deposition of these metals: Spearman rank correlation coefficients were between 0.62 and 0.67, and 0.67 and 0.73 for cadmium and lead, respectively (p?<?0.001). Multivariate decision tree analyses showed that cadmium and lead concentrations in mosses were primarily determined by the atmospheric deposition of these metals, followed by emissions of the metals. Low to very low correlations were observed between mercury concentrations in mosses and modelled atmospheric deposition of mercury. According to the multivariate analyses, spatial variations of the mercury concentration in mosses was primarily associated with the sampled moss species and not with the modelled deposition, but regional differences in the atmospheric chemistry of mercury and corresponding interactions with the moss may also be involved.

Conclusions

At least for cadmium and lead, concentrations in mosses are a valuable tool in determining and mapping the spatial variation in atmospheric deposition across Europe at a high spatial resolution. For mercury, more studies are needed to elucidate interactions of different chemical species with the moss.     

Recovery from acidification in Lake Örvattnet,Sweden

Lake Örvattnet has been monitored extensively for both chemical and biological variables since 1967. The lake acidified during the 1960's and pH was mostly below 5 throughout the 1970's. Due to the acidification, peat moss (Sphagnum spp.) expanded over the lake bottom and the only surviving fish species was perch (Perca fluviatilis), but it experienced reproduction problems. In the mid 1980's, the Sphagnum cover collapsed, and by 1989 it had almost disappeared. There has been a clear recovery of the perch population. Recovery of the lake is also recorded by diatom assemblages in the lake sediment. Diatom-inferred pH increased from 4.7 to 4.9. The development of measured lake-water pH is unclear, but acid episodes in spring have become less severe. By 1993, atmospheric sulphate deposition had decreased by 30–40% in this area of Sweden compared to the late 1960's. Lake-water sulphate concentrations have decreased by ～30% since the 1960's. Nitrogen deposition has increased over the last decades, but is not yet contributing to lake acidification. No major land-use changes have occurred and changes in hydrology cannot explain the observed changes in chemistry and biology. We ascribe the recent recovery in the lake to reduced deposition of sulphate. In conclusion, Lake Örvattnet has begun to recover from acidification.     

Determining baselines and variability of elements in plants and soils near the Kenai National Wildlife Refuge,Alaska

Recent investigations on the Kenai Peninsula had two major objectives: (1) to establish elemental baseline concentrations ranges for native vegetation and soils; and, (2) to determine the sampling density required for preparing stable regional geochemical maps for various elements in native plants and soils. These objectives were accomplished using an unbalanced, nested analysis-of-variance (ANOVA) barbell sampling design. Hylocomium splendens (Hedw.) BSG (feather moss, whole plant), Picea glauca (Moench) Voss (white spruce, twigs and needles), and soil horizons (02 and C) were collected and analyzed for major and trace total element concentrations. Using geometric means and geometric deviations, expected baseline ranges for elements were calculated. Results of the ANOVA show that intensive soil or plant sampling is needed to reliably map the geochemistry of the area, due to large local variability. For example, producing reliable element maps of feather moss using a 50 km cell (at 95% probability) would require sampling densities of from 4 samples per cell for Al, Co, Fe, La, Li, and V, to more than 15 samples per cell for Cu, Pb, Se, and Zn.     

Microbial activity and functional composition among northern peatland ecosystems

The extent to which complex interrelationships between plants and microorganisms influence organic matter dynamics is critical to our understanding of global C cycles in changing environments. We examined the hypothesis that patterns of soil microbial activity and functional composition differ among vegetation types in northern peatland ecosystems. Microbial characteristics were compared among peatlands differing in plant growth form (tree, shrub/moss, sedge) in two regions (New York State and West Virginia). Microbial activity (basal respiration) was greater in surface (0-15 cm) than subsurface (15-30 cm) peat and from sites dominated by shrubs and Sphagnum moss (3.9±0.65 μg C g⁻¹ h⁻¹) compared to forested (1.8±0.20 μg C g⁻¹ h⁻¹) or sedge-dominated sites (1.9±0.38 μg C g⁻¹ h⁻¹). Microbial activity was not related to decomposability of peat organic matter among vegetation types, and activity was unexpectedly higher in sites with lower peat pH and higher water table level. Substrate-induced respiration (SIR) did not show a clear pattern among vegetation types, but was greater in surface than subsurface peat. Microbial responsiveness to added glucose was very low. The ratio of basal respiration to SIR varied between 0.39 and 0.72 and, like activity, was highest in shrub/Sphagnum sites. Microbial substrate utilization patterns (assayed with BIOLOG^® GN plates) also differed between shrub/Sphagnum sites and forest or sedge sites, suggesting that C fluxes were mediated by different assemblages of microorganisms in shrub/Sphagnum peatlands. Principal component (PC) scores indicated more utilization of N-containing compounds and carboxylic acids, and less utilization of carbohydrates by microbial communities in shrub/Sphagnum sites. PC scores were much more variable both within and among vegetation types for sites in West Virginia than in New York State, and a greater diversity of C sources were utilized in WV (57±3) than NYS (47±2) peat. Our results suggest a link between microbial respiratory activity and microbial functional composition as they vary among these peatland vegetation types.     

Growth and Production of Aquatic Mosses in Acidified Lakes of Karelia Republic,Russia

Three small acidified lakes (pH of water 5.3–5.9) in Karelia Republic, northwestern Russia, were studied in respect to speciescomposition, phytomass, and morphometric characteristics of aquatic mosses in their dense carpet. The dense moss carpet inlake L1 (mainly, Sphagnum denticulatum Bird.) occurred at a depth of 5.0–7.5 m and covered about 50% of the bottom area. The monospecific moss carpets occurred in lake L2 (Warnstorfia exannulata s. lato) and lake L3 (Fontinalishypnoides Hartm.) at depths of 5.0–7.0 m and 4.5–5.5 m and covered 20 and 13% of the bottom, respectively. The moss phytomass was 43–53 g air-dry mass m^-2 in the lake L2 andlake L3, while it was much higher in lake L1 – 293 g m^-2.Seasonal changes in shoot morphology of S. denticulatum,W. exannulata s. lato and in size and density of leavesalong the shoot axis of F. hypnoides allowed to reconstructthe annual growth and to estimate of growth rates of the mossesin their natural habitat within dense carpet. The absolutely netproduction of the mosses was estimated on the basis of thesedata. In two lakes (L2 and L3), the annual means of absolutelynet production of the aquatic mosses were 32–41 g air-dry massm^-2 yr ^-1, while in the third lake (L1) they weremarkedly higher – 157 g m^-2. The obtained results andcharacteristics of aquatic mosses are compared with those formosses in acidified Lake Grane Langsø in Denmark.     

Accumulation Capacities of Particulate Matter in an Acrocarpous and a Pleurocarpous Moss Exposed at Three Differently Polluted Sites (Industrial, Urban and Rural)

The aim of this study was to compare the capacity of two morphologically different moss species to accumulate elements when exposed to three different types of air pollution (rural, urban and industrial). Transplants of Pseudoscleropodium purum and Ceratodon purpureus were exposed for 6 months, and the concentrations of 18 elements (Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, As, Mo, Cd, Sn, Sb, Ba, La, Pb and Bi) in the mosses samples were analysed by inductively coupled plasma–mass spectrometry. On the whole, the metals were accumulated by mosses, and this accumulation was correlated with concentrations in the atmospheric particles. Whereas P. purum is to be preferred for Al, Cu, Zn and Fe monitoring, C. purpureus was most efficient at accumulating Mo, Ti, V, As, Sn, La and Pb. In both species, a phenomenon of saturation was observed during the exposure at the most contaminated site (industrial).     

Estimation method of residual alkylating agents in water treated with chloring-containing oxidant

Concentrations of trace metals in mosses Hylocomium splendens (Hs) and Pleurozium schreberi (Ps) are compared along with wet deposition at 8 sites in Sweden. Cd, Mn, Zn and Cr concentrations were similar in both mosses, while Cu, Fe, Pb, Ni and V levels were 14 to 24% higher in Hs than in Ps. The comparison to wet deposition estimates indicates that concentrations in mosses are also influenced by other factors than the adsorption of precipitation. No correlation was observed between the wet deposition of Mn, Cr and Ni and moss concentrations.     

Contrasting the geochemistry of aluminum among peatlands

Aluminum concentrations were measured in surface waters, pore waters and surface peats of 15 wetlands in south-central Ontario. Wetlands were grouped floristically and chemically as mineralpoor, moderately-poor or mineral-rich fen. Mineral-poor fens were dominated bySphagnum, were low in alkalinity (0.31μeq L^?1) and pH (4.5–6.3). Moderately-poor fens had a mixture of vegetation (Sphagnum, sedges and grasses), mid-alkalinity (23–91μeq L^?1) and pH (5.8–6.4). Mineral-rich fens were dominated by sedges and grasses, had high alkalinity (104–181μeq L^?1) and circumneutral pH (6.2–6.3). Surface water Al concentrations were less in mineral-poor versus moderately-poor and mineral-rich fens (F=32.0; P<0.05). Pore water Al concentrations were lower in 4 of 5 mineral versus the mineral-rich fens (F=92.15; P<0.05). In all but two cases pore water Al (all species <0.2μm) were greater within the fen peats versus the overlying surface waters suggesting that peats could act as a source of Al to the overlying waters. In all wetlands, 70 and 30% of peat Al was recovered by a hydroxylamine hydrochloride/acetic extract (primarily inroganic) and an ammonium hydroxide extract (primarily organic), respectively. Differences in “extractable” Al recovered by the two reagents (i.e., inorganic+organic Al) among the 15 wetlands were independent of wetland type. Distribution coefficients, k _d , were different among the 3 types of wetlands (F=25.0; P<0.05) with theSphagnum dominated mineral-poor fens containing higher values versus the sedge and grass dominated mineral-rich fens. Lower surface and pore water concentrations of Al in mineralpoor versus mineral-rich fens may in part be a result of differences in the degree of minerotrophic influences between the two types of peatlands. As well, the greater binding capacity ofSphagnum peat as indicated by higher k _d 's in the mineral-poor fens, may have contributed to the observed lower pore water and surface water Al concentrations in mineral-poor versus mineral-rich fens. It has been postulated that anthropogenic acidification of peatlands will accelerate the transformation of a mineral-rich fen to that of a mineral-poor fen and ultimately to bog. Changes in Al geochemistry that may ensue as this transition occurs include decreases in pore and surface water Al concentrations with concurrent increases in peat bound Al.     

Specifics and Temporal Changes in Air Pollution in Areas Affected by Emissions from Oil Shale Industry, Estonia

Atmospheric air pollution levels and long-term effects on the environment caused by simultaneous presence of SO₂ and oil shale alkaline fly ash during the last five decades (since 1950) were investigated. The annual critical value of SO₂ for forest (20 µg m^?3) was surpassed in 1% (～35 km²) of the study area where the load was 30–40 µg m^?3. No effect of long-term SO₂ concentrations of up to 10–11 µg m^?3 (0.5-h max up to 270 µg m^?3) and simultaneous fly ash loads of up to 95 µg m^?3 (1000 µg m^?3) on the growth and needle longevity of Pinus sylvestris was established. The yearly deposition (average load up to 20–100 kg S ha^?1) was alkaline rather than acidic due to an elevated base cation deposition in 1960–1989. Since 1990, the proportion of SO₂ in the balance of components increased: about 70–85% of the total area was affected while the ratio of annual average concentrations of SO₂ to fly ash was over 1. The limit values of fly ash for Sphagnum mosses and conifers in the presence of SO₂ are recommended.     

Accumulation of Polycyclic Aromatic Hydrocarbons in Soils and Mosses of Southern Tundra at Different Distances from the Thermal Power Plant

A number of polycyclic aromatic hydrocarbon (PAH) structures have been identified in organic horizons of surface-gley tundra soils (Stagnic Cambisols) and the moss Pleurozium schreberi. The total content of polyarenes in soils and P. schreberi exceeds the background values in 3.5–5 times. A tendency of increasing content of polyarenes with the distance from the source to 1 km has been revealed. High coefficients of variation have been found between the contents of PAHs in snow cover, organic soil horizons, and mosses. Light hydrocarbons dominate in the composition of PAHs from the snow and ground covers and mosses. Naphthalene dominates on the surface of mosses in all of the studied plots, which is largely related to its intensive uptake by mosses under pollution conditions. It has been found that when the input of polyarenes onto the surface of tundra phytocenoses increases, the bioaccumulation of PAHs by P. schreberi is intensified, and PAHs begin to penetrate into moss. The increase in the concentration of high-molecularweight polyarenes in the environment plays the key role in the activation of PAH bioaccumulation by moss. It has been shown that P. schreberi can be used as an indicator species for monitoring the contamination of tundra phytocenoses by polyarenes. Both living and dead parts of P. schreberi are suitable for the environmental monitoring of PAH contamination.     

Sunflower ( Helianthus annuus L.) Seeding Rate Additions to Forage Oat-Legume Mixtures in Newfoundland

Lingonberry (Vaccinium vitis‐idaea L.) cvs “Sussi”; and “Sanna”; were cultivated on mineral soil with four different soil surface treatments (Sphagnum peat mulch, sand mulch, plastic mulch and herbicide 3‐syclohexyl‐5, 6‐trimethylenurasil (lenasil)). Amount of annual weeds, plant coverage and yield were observed over five years. Weeds were most abundant in the first two observation years. Sand mulch was the least efficient for the control of annual weeds for both cultivars, whereas lenasil was the most efficient for “Sussi”;, and peat mulch for “Sanna”;. The plant coverage increased steadily throughout the years in the “Sussi”; plots, especially in plots mulched with peat. The spreading of “Sanna”; was slower in all treatments. It was best in plots mulched with peat or sand. Overall, “Sanna”; was more productive, with the highest yield on sand mulch and the lowest on lenasil‐treated plots. “Sussi”;, instead, yielded best on lenasil plots and poorest on sand.     

Use of msses as collectors of airborne heavy metals near a smelting complex

Moss bags are used as collectors of airborne heavy metals in the region surrounding the Zn and Pb smelting complex at Avonmouth, near Bristol, U.K. A land area of 660 km' is studied by exposure of 250 freshly prepared Sphagnum moss bags for 6-week periods. The results are presented as a series of squares computer drawn on maps of the area. Concentrations of metals in exposed mosses range from 4800 ppm Pb, 8200 ppm Zn and 200 ppm Cd, ≈ 700 m from the smelter, to insignificant levels in areas of Wales further than 15 km from the smelter. Metal concentrations are high within the zone of the prevailing winds from Avonmouth, where Pb and Cd values exceed background levels approximately 15-fold, as far as 15 km from the smelter.     

The acid-base balance of peatlands: a short-term perspective

Acidity budgets for an artificially acidified and an unacidified peatland in mid-continental North America are dominated by the production and export of organic acids. A fraction (about 50%) of these acids are neutralized by alkalinity from atmospheric deposition and upland run-off. The acid applied to the experimentally acidified site is neutralized by uptake of nitrate and sulfate. Short-term measurements show that nitrate is taken up rapidly in surface layers of moss while sulfate penetrates more deeply into the peat. Sulfate retention within the two sites ranges from 56 to 70% on an annual basis. Stripping of basic cations is shown to result from acid application to base-rich peat. These results suggest that short-term effects of acid deposition on peatlands will be slight, but long-term site acidification is possible.     

Mass loss and nutrient release during litter decay in peatland: The role of microbial adaptability to litter chemistry

In peatlands the reduced decomposition rate of plant litter is the fundamental mechanism making these peat-accumulating ecosystems effective carbon sinks. A better knowledge of litter decomposition and nutrient cycling is thus crucial to improve our predictions of the effects of anthropogenic perturbation on the capacity of peatlands to continue to behave as carbon sinks. We investigated patterns of plant litter decomposition and nutrient release along a minerotrophic-ombrotrophic gradient in a bog on the south-eastern Alps of Italy. We determined mass loss as well as P, N, K, and C release of seven vascular plant species and four moss species after 1 year in both native and transplanted habitats. Hence, differences in litter decay were supposed to reflect the degree of adaptability of microbial communities to litter quality. Polyphenols/nutrient and C/nutrient quotients appeared as the main parameters accounting for decomposition rates of Sphagnum litter. In particular, litter of minerotrophic Sphagnum species decomposed always faster than litter of ombrotrophic Sphagnum species, both in native and transplanted habitats. Decomposition rates of vascular plant litter in native habitats were always higher than the corresponding mass loss rates of Sphagnum litter. Minerotrophic forbs showed the fastest decomposition both in native and transplanted habitats in accordance with low C/P and C/N litter quotients. On the other hand, C/P quotient seems to play a primary role also in controlling decomposition of graminoids. Decomposition of deciduous and evergreen shrubs was negatively related to their high lignin content. Nitrogen release from Sphagnum litter was primarily controlled by C/N quotient, so that minerotrophic Sphagnum litter released more N than ombrotrophic Sphagnum litter. Overall, we observed slower N release from litter of ombrotrophic vascular plant species compared to minerotrophic vascular plant species. No single chemical parameter could predict the variability associated with different functional groups. The release of K was very high compared to all the other nutrients and rather similar between ombrotrophic and minerotrophic litter types. In Sphagnum litter, a higher C/P quotient was associated with a slower P mineralisation, whereas a faster P release from vascular plant litter seems primarily associated with lower C/P and polyphenols/P quotients.     

Soil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlands

Rates of organic carbon mineralization (to CO₂ and CH₄) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid‐boreal Alberta, Canada, two were in low‐boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH₄ production varied significantly as a function of peat type, transplant site, and the type–site interaction. All four peat soils had very small rates of CH₄ production (< 20 nmol g^?1 day^?1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH₄ production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH₄ production (4000 nmol g^?1 day^?1) correlated with large holocellulose content, a large concentration of p‐hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO₂ production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO₂ production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH₄ and CO₂ in Sphagnum‐derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future.     

Statistical models for the accumulation of PAH,chlorinated hydrocarbons and trace metals in epiphytic Hypnum cupressiforme

Concentrations of PAH (1.12-benzoperylene, 3.4-benzopyrene, fluoranthene), chlorinated hydrocarbons (α-BHC, lindane, PCB) and trace metals (Zn, Pb, Cu) in bulk precipitation, as well as PAH and trace metal concentrations in atmospheric dust samples from 14 sites in Bavaria, F.R.G. are presented for two vegetation periods (1979 and 1980). The same substances were also analyzed in epiphytic moss (Hypnum cupressiforme var. filiforme) sampled from tree trunks in October 1979 and 1980. Using mean immission values and the amount of precipitation as predictors and concentrations of pollutants in moss samples as criteria, a number of multiple regression models were computed in order to quantify the relationships between absolute air pollution data and accumulated trace substance values. Beta values of all variables help to determine whether bulk precipitation or atmospheric particulate matter has dominant influence on the uptake of trace substances by mosses. The study shows that epiphytic mosses can be used to monitor both heavy-metal, PAH and chlorinated hydrocarbons.     

Microbial Community and Rate of Cellulose Decomposition in Peat Soils in a Mire

A field survey was carried out from April to October, 1992 in the Miyatoko Mire in Fukushima Prefecture, Japan, to determine the characteristics of the microbial community and cellulose decomposition rates in the peat soil. A total of 14 study sites were selected, including three types; hummocks (type I), hollows covered with Sphagnum (type II), hollows and streams without Sphagnum (type III). The numbers of fungi (2-1,000×10⁴ CFU g^-1) and bacteria (8.5-9,000 ×10⁵ CFU g^-1) varied with the sites and sampling dates: seasonal fluctuations were especially high in hummocks. The numbers of cellulolytic fungi (4.7-300×;10⁴ CFU g^-1) and cellulolytic bacteria (1.5-9.2×10⁵ CFU g^-1) also differed between sites. Cellulolytic fungi were predominant in the Sphagnum peat of type I, while cellulolytic bacteria were predominant in the peat soil of type III. Decomposition rates of cellulose filter paper for the 6 month period ranged from 0.01 to 0.83, and tended to be higher in the peat of type II than type I.     

Role of cation exchange in preventing the decay of anoxic deep bog peat

The major bog systems in northern areas are dominated by Sphagnum species, the partially decomposed remains of which form the bulk of deep peat. By adding mono- and di-valent cations to deep peat cores (2.0-2.5 m) and measuring CH₄ and CO₂ concentrations in the manipulated peat cores using quadrupole mass spectrometry (QMS) we demonstrate that the lack of availability to microorganisms of essential cations is limiting decay in deep peat. The cations with the highest binding strength displaced the most cations and stimulated decay. Decay in deep peat cores was also stimulated by a C source (acetate), but not by NH₄⁺. The addition of cations and acetate resulted in a less than additive stimulation of decay. The stimulatory effect of acetate and copper decreased in the presence of ammonium. The addition of EDTA to surface bog peat (where cations are conserved) decreased decay rates in surface peat (0.0-0.5 m) to that of the untreated deep peat (2.0-2.5 m). Deep peat was unaffected by treatment with EDTA. The effect of adding Cu²⁺differed with the depth from which the peat was collected. Cu²⁺ did not stimulate decay in surface bog peat (0.0-1.5 m) but stimulated decay in peat from 1.5-3.5 m. Below 3.5 m to the bottom of the profile (5.0 m) no positive effect was observed. By comparing deep peat with surface peat we have shown that cation limitation because of high cation exchange capacity is specific to the main mass of deep bog peat and may explain differences in decay rates between anoxic surface peat and deep peat.